The N-methyl pyrrolidone (called “NMP” for short), is one of the important industrial chemicals and widely applied in various fields such as petroleum chemical industry, agricultural chemical, medicine and electronic material.
In the prior art, the N-methyl pyrrolidone is obtained through heating, pressurization and dehydration of N-methyl-4-hydroxyl butyryl amide which is produced by the reaction of the gamma-butyrolactone and methylamine, and this is the only industrial process for producing N-methyl pyrrolidone, and used by corporations such as American GAF, German BASF and the Japanese Mitsubishi and so on for mass production. Since the difference between boiling points of the NMP and raw material gamma-butyrolactone is only 2 degree C., it is very difficult to separate the two reagents above by method of rectification.
The U.S. Pat. No. 4,965,370 and the European patent EP 346086A2 disclosed the method for preparing highly purified NMP by adding alkaline metal or alkaline metal salt to reduce the acidic compound content of the reaction solution of NMP. The high purity NMP was then obtained by distillation.
Japanese patent JP06-279401A and JP08-109167A both use repeated distillation to obtain high purity NMP. However, it is difficult to produce NMP on the large scale through using the methods above because of their high cost and high energy consumption, difficult process control and high risk.
The prior art includes the preparation of N-substituted 2-pyrrolidones from a large number of compounds by catalytic hydrogenation. The starting compounds concerned are mixtures of a primary amine (II) and maleic anhydride (DE-A 4,018,243, U.S. Pat. No. 3,109,005) or fumaric acid, maleic acid, succinic acid, functional derivatives of these acids such as succinic anhydride, or amides, imides derived from the reaction of II with the acids as mentioned above, all of which can be hydrogenated to produce N-substituted 2-pyrrolidones (U.S. Pat. No. 5,434,273). Irrespective of the nature of these starting materials the reaction mixtures obtained after hydrogenation are worked up by distillation to obtain the pure product.
Olsen, in U.S. Pat. No. 4,814,464 described process for making N-alkylpyrrolidones from a maleic derivative or a succinic derivative which involves conversion of succinic anhydride to N-alkylsuccinimide by ammonolysis-alkylation with alkanol and ammonia, and catalytically reducing the resulting N-alkylsuccinimide to the N-alkylpyrrolidone.
Olsen, in U.S. Pat. No. 4,841,069 described reactions of succinic anhydride, methanol, ammonia and hydrogen to obtain NMP. Olsen described a reaction between succinic anhydride, methanol, and ammonia, and 700 psig of hydrogen in presence of 5% palladium on carbon catalyst, were heated 21 hrs at 290° C. with stirring. Olsen reported that 100% of the succinic anhydride was converted with 60% selectivity to N-methyl succinimide and 30% selectivity to N-methyl pyrrolidone.
Olsen, in U.S. Pat. No. 4,814,464 described the similar ammonolysis-alkylation reactions in which a succinic derivative such as the anhydride, acid or diester is reacted with ammonia and a C1 to C4 alkanol to give corresponding N-alkylsuccinimide. The N-alkylsuccinimide can be reduced catalytically with hydrogen either continuously or batch-wise to obtain NMP.
Koehler et al., in U.S. Pat. No. 5,101,045 described a process for the preparation of N-substituted pyrrolidones by catalytic hydrogenation of maleic anhydride, maleic acid and/or fumaric acid in the presence of ammonia, a primary alcohol and a modified cobalt oxide catalyst. In Example 3 of the patent, it has been stated that 75 ml of a 45% aqueous diammonium maleate solution and 75 ml methanol were hydrogenated for 42 hours at 230 C. in the presence of 10 g of a modified cobalt oxide catalyst to produce NMP in 89% yield.
Several patents such as U.S. Pat. No. 3,080,377; U.S. Pat. No. 3,198,808; U.S. Pat. No. 3,681,387 and U.S. Pat. No. 4,263,175 described the hydrogenation of succinic acid or anhydride in the presence of ammonia to yield 2-pyrrolidones. Catalysts used for the said synthesis include, the palladium on carbon, ruthenium on carbon, ruthenium on alumina, and cobalt oxide.
Chichery et al., in U.S. Pat. No. 3,448,118; Weyer et al. in U.S. Pat. Nos. 5,157,127 and 5,434,273 disclosed methods of making N-substituted pyrrolidones in which succinic acid or anhydride or the like is hydrogenated in the presence of a primary amine.
Jr. Fyre in EP patent 2210877 A1 described a process for the synthesis of pyrrolidone especially NMP via hydrogenation of succinic anhydride, succinic acid, or the like in presence of a catalyst comprising two metals in aqueous conditions.
All the aforementioned processes have the disadvantage either that the synthesis of intermediate imide requires longer reaction time, high reaction temperature or that the poor yield of the product. Further the aqueous nature of the methylamine provides unsatisfactorily low yields and impure product.
Synthesis of cyclic imides from the reaction of cyclic anhydride with hydroxylamine hydrochloride using 4-N,N-dimethylaminopyridine (DMAP) as catalyst under microwave irradiation is reported in the literature (Molecules, 2008, 13, 157-169). However, this method is associated with some drawbacks such as requirement of catalyst, higher reaction temperature and using only hydroxylamine hydrochloride.
Workers at the Pacific Northwest National Lab (PNNL) have developed a simple multi-step process involving both catalytic and non catalytic reactions which converts succinic acid into NMP. The developed process consisted two essential steps, i.e. non-catalytic (thermal) conversion of diammonium succinate (DAS) and methanol to n-methyl succinimide (NMS) followed by hydrogenation of the NMS to NMP. They have reported rhodium based catalysts for the hydrogenation of N-methylsuccinimide to N-methyl-2-pyrrolidone, which are highly expensive.
The drawbacks of the hitherto known processes such as higher energy inputs, longer reaction times, high temperature, lower conversion and poor selectivity, evident the necessity for the development of an improved process for the synthesis of N-methyl pyrrolidone.
It has been well established that using microwave irradiation reduces the reaction time as compared to the traditional synthesis by several hours, which allows the preparation to be achieved by using less energy inputs and shorter reaction time.